In the ink-jet recording, micro droplets of an ink are filed by various driving principles to record images and characters. The ink-jet recording method has merits such as that the high speed, low noise and multi-color recording can be easily attained.
The ink-jet recording using a dye ink is spread accompanied with nearing the image quality to that of silver salt photograph and the lowering of the price according to the recent progress of the technology.
The dye is soluble in a solvent, and the dye molecular forms color in a state of a molecular or a cluster. Accordingly, the absorption spectrum is sharp and the color is highly pure and clear since the surroundings of the molecules are similar with each other. The ink-jet image with high transparent feeling and clear hue can be obtained by the dye ink since granular pattern caused by the presence of particles is not formed and scattered or reflected light is not occurred. Moreover such the ink has a high reliability with respect to that the blocking of the printer is difficultly occurred. Thus the dye ink has been most commonly used.
On the other hand, the dye ink has a drawback such as that the color fastness is low because the reducing of the number of the molecules directly reflects to the color density when the molecule is decomposed by a reaction such as photochemical reaction. The image recorded by the ink-jet using the dye ink is unavoidably limited in the use and degraded in the quality since the ink is an aqueous solution of a dye and easily spread on the recording medium even though high image quality can be obtained. The dye ink further has a problem that the dye ink is permeable into the recording medium so that high density difficultly can be obtained compared with an ink using a pigment.
The pigment ink, in which the pigment having high light fastness is used as the colorant, is applied for the use requiring an image with high fastness. However, the pigment ink is inferior in the color reproducibility to the dye ink since the pigment exists in a state of pigment particles. Therefore, the pigment more easily scatters light compared with the dye and gives the image with low transparent feeling.
As the means for solving the above-mentioned problems of the aqueous ink using the water-soluble dye, addition of fine resin particles such as emulsion and latex has been investigated. Japanese Patent Publication Open to Public Inspection, hereinafter referred to as JP O.P.I. Publication, No. 55-18418 describes a proposal relating to a recording medium for ink-jet recording in which latex defined as “a kind of colloid liquid formed by dispersing a component such as rubber and resin by a emulsifying agent in a state of fine particle in water”. An amount of latex two times or more of the mount of the dye is necessary to improvement the light fastness and the spread prevention by the addition of the latex such as that proposed in the publication. Consequently, the stability of the dispersion and the release of the ink are difficultly held and the image equal to that by the silver salt photography in the granularity and the glossiness cannot be obtained yet.
Inks for ink-jet recording containing aqueous dispersion of resin colored by an oil-soluble dye or a hydrophobic dye are proposed for solving the problems of low image density and the low light fastness of the aqueous ink using the water-soluble dye. For example, JP O.P.I. Publication Nos. 55-139471, 58-45272, 3-250069, 8-253720, 8-92513, 8-183920 and 2001-11347 each proposes an ink using emulsion polymerized polymer or dispersed polymer particle each dyed by the oil-soluble dye. In such the ink using the colored fine particles, the effects of the ink is reduced when the dye is at the surface or outside of the particle. Moreover, problems of the reducing of the image glossiness, increasing of image spreading and lowering of the adhesiveness between the recording medium and the image formed thereon are newly found when the recorded image is stored for a long period under high humidity.
As the method for raising the penetration speed of the ink into the ink-jet recording medium and improving the anti-spreading ability and the glossiness, it has been known to use a solvent capable of lowering the dynamic surface tension of the ink such as triethylene glycol monobutyl ether. However, in the aqueous ink containing the colored particle which is comprised of colorant included in the resin, the solvent such as triethylene glycol monobutyl ether is penetrated into the resin constituting the colored fine particle so as to solve out the colorant included in the resin to the aqueous medium of the ink. Therefore, lowering of the image density, blocking of the ink-jet head, adhering of the recording medium surface, lowering of the penetration speed of the ink into the recording medium, overflowing of the ink and occurring of unevenness of the image are caused. Accordingly, the using amount of the solvent capable of lowering the surface dynamic tension of the ink is inevitably limited.
As above-mentioned, the aqueous ink containing the colored fine particle using the oil-soluble dye or the pigment has various problems and is required to further improvement even though it has latent possibility of solving the problems of the usual aqueous ink using the water-soluble dye or the pigment dispersion.